Viewed nose-on, a typical fighter aircraft has a radar cross section (RCS) on the order of one square meter. A similarly viewed low observable aircraft may have an RCS of only 0.01 square meter. Unless special RCS reduction measures are employed, even a comparatively small planar array antenna can have an RCS of up to several thousand square meters when viewed from a broadside direction! Since an aircraft's radome is transparent to radio waves, if stealth is required, steps must be taken to reduce the RCS of the installed antenna. In this chapter, we will be introduced to the sources of reflections from a planar array antenna, learn what can be done to reduce or render them harmless, and see why these steps are facilitated in an ESA. We will then take up the problem of avoiding so-called Bragg lobes, which are retrodirectively reflected at certain angles off broadside if the radiator spacing is too large compared to the radar's operating wavelength. Finally, we will very briefly consider the critically important validation of an antenna's predicted RCS.